Three dimensional objects have been manufactured using fused filament fabrication techniques in which a fabrication material is heated to a flowable state and is deposited upon previously deposited solidified layers of the material in a pattern determined based upon design information provided within a mathematical computer aided design (CAD) model. The material is heated to the flowable state and is deposited layer-by-layer upon previously deposited layers that have cooled sufficiently to be in a sufficiently solidified state to provide a structurally stable layer for deposition of a new layer. Each successive newly deposited layer cools, solidifies and adheres to a previously deposited layer of material with an adequate bond upon solidification. In this manner, layers of material progressively build up and solidify to form a three-dimensional object resembling the CAD model.
The fabrication material is fed to a print head, sometimes referred to as an extrusion head, that inputs the material in a solid state, heats it to a flowable state, and outputs the fabrication material in the flowable state for deposition in the pattern determined by the CAD model. The print head ordinarily includes a liquefier, a dispensing nozzle and a drive mechanism. The drive mechanism drives the material in a solid state to the liquefier and out through the nozzle in a liquid state.
In the past, a drive roller and idler roller pair have been used to advance a flexible filament fabrication material through print head. As the roller pair advanced the filament into the print head, the force of the incoming filament strand extrudes the flowable material out from the dispensing nozzle where it is deposited onto previously extruded solidified layers of the material mounted upon a build platform. The flow rate of the material extruded from the nozzle is a function of the rate at which the filament is advanced to the head and the size of the dispensing nozzle orifice.
The print head typically is moveably mounted upon a support structure. Motors are provided to move of the print head within a horizontal x, y plane parallel to the build platform and to move the platform in a vertical z-direction perpendicular to the plane of movement of the print head. An electronic controller controls the motors to control movement of the print head in the horizontal plane and to control z-direction movement of the build platform. The controller also controls the rate at which the drive mechanism advances the material through the print head. By controlling these processing variables in synchrony, the material is deposited at a desired flow rate in pattern, layer-by-layer, in areas defined from the CAD model. The dispensed material solidifies upon cooling to create a three-dimensional solid object.
The dispensing nozzle often is incorporated as a part of a disposable component sometimes referred to as a ‘hot end’ in which the phase transformation of a filament from solid to liquid occurs. The dispensing nozzle is formed of a highly heat conductive metal, typically brass. The filament is fed to the nozzle though an elongated pipe, or barrel, also formed of metal. The phase transition takes place within the pipe. A solid state filament material is fed in one end of the metal pipe, and liquid state material flows out from the other end of the pipe to the dispensing nozzle. The disposable component comprising the dispensing nozzle periodically requires replacement because foreign matter accumulates inside resulting in irregular flow or even blockage. For example, solid fragments of the modeling material may become lodged inside the pipe due to turning on and off the liquefier resulting in molten material solidifying within the component.